Typical data storage libraries use mechanical robots and/or linkages to pick and place data storage cartridges into media drives and empty cartridge slots. Freedom of movement of the robotics is governed by the mechanical constraints of the system, and is limited by the nature of design to be a function of the number of directions (axis) of movement required. In most cases, a data storage library layout is structured around the desired cost and complexity of the robotics. Designers are limited in the storage media cartridge selection and design options by the robotics freedom of movement.
Robotic movement is controlled by some type of actuator, where the number of actuators is often equal to, but not limited by the number of directions the robot moves. The robot is often a self-supporting mechanism having a picker assembly at the end of an arm that can be moved in two or more directions. The picker assembly is positioned in proximity to the cartridge slot or media drive using electronic encoders on the actuators, or using an optical position sensor at the end of the arm. Correcting for positional errors of the picker assembly result in excess wear and lower reliability of the robot.
Some attempts have been made to alleviate the constraints of stand alone robotic arms by implementing carousel structures, draw cable devices, and track/rail type systems. These systems have some sort of track or guide rail and a carriage that moves the storage media cartridges to and from the media drives. The track forms a guide path that directs the carriage to any desired position, be it in the continuous loop of a carousel, a straight line following a draw cable, or other combinations of straight and curved sections. Positioning errors of the cartridge are limited to one direction, that direction being along the length of the track.
Carriage and track system configurations are limited by the geometry of the track, in particular curved sections, and the number of mechanical contacts the carriage make to the track. Tracks with broad curves may not fit the allocated space claims. Tracks with sharp curves are difficult for the carriage to traverse. The mechanical contacts between the carriage and tracks are typically wheels with horizontal axis of rotation. The nature of such wheels is to bind when forced into corners. An alternate solution is to use pairs of wheels with vertical axis of rotation to pinch sideways on a guide rail. While this solves the cornering problem, the number of wheels and other support points requires may not be desirable. A third solution uses guide wheels tipped at an angle, or wheels with V-shaped grooves, to carry the carriage around corners. In these situations, the loads imposed on the wheels by the mass of the carriage may cause the wheels to lift off of the rails causing derailments.
A track/guide rail and carriage guidance mechanism is desired having the design flexibility to include both straight and curved sections in the track, including sharp corners. The preferred solution has a minimal number of contacts between the carriage and track while allowing for high speed carriage movements and stability around sharp corners.